That would echo my experience. With the drillings of typical configuration we get two cold barrels trying to keep a hot barrel from moving. With the several I've had generally there isn't much movement until the 3rd shot but, it isn't much, though continued shooting and they will walk quite a bit. How likely is it a fella will shoot 3 times at game with a single shot rifle? As you said, with hunting firearms it isn't a problem.

The only double rifle I have that moves much is that Erfurt in 11.15 X 60R and that's a function of a clean, cold bore vs a fouled by BP bore. There again, two shots and game and reload....a 3rd isn't likely. Fortunately, in 60 years of hunting, a 3rd has never been necessary....and rarely a 2nd. Now watch me have just jinxed myself.